Posted
by
samzenpuson Thursday May 15, 2014 @08:11PM
from the step-by-step dept.

sciencehabit (1205606) writes "If the clock rewound, would organisms evolve the same way they did before? Humble stick insects may hold the answer to that long-running question in biology. Through studies of these bugs, whose bodies match the leaves the insects live on, researchers have found that although groups of the bug have evolved similar appearances, they achieved that mostly via different changes in their DNA. 'I think it says that repeatability of evolution is very low,' says Andrew Hendry, an evolutionary biologist at McGill University in Montreal, Canada, who was not involved with the work."

Just look at how many times Eyes have independently evolved, yet they all have the same basic components.

We put water, methane, CO2, etc. in a closed system, ran some simulated "lightning" through, and got amino acids and what not forming. Various experiments show similar (even more prominently supporting) results: Nature and physics shapes the beings that exist within it.

There are plenty of other examples of evolution coming to similar results from different ends -- Just look at the shapes of sharks and w

This tells us that getting a sensor is repeatable. There are high-level design details of eyes that are divergent across species. The "blind spot" is a flaw in the eye design that is shared by all vertebrates, but cephalopods don't have it. Either it's very hard to mutate our way out of the flaw, or the flaw is by itself not important enough for the extraordinarily rare mutants who evolve their way past it to gain any ground on non-mutant populations.

It's easy to think of that as an accident of fate, and eventually such accidents are bound to build up into going a different direction in response to strong selection pressures.

I think sharks and dolphins is better than sharks and whales. That demonstrates convergent evolution -- but note that dolphins still have lungs, and sharks still have gills. They got to similar body plans but they are not fundamentally the same.

This tells us that getting a sensor is repeatable. There are high-level design details of eyes that are divergent across species. The "blind spot" is a flaw in the eye design that is shared by all vertebrates, but cephalopods don't have it. Either it's very hard to mutate our way out of the flaw, or the flaw is by itself not important enough for the extraordinarily rare mutants who evolve their way past it to gain any ground on non-mutant populations.

If an eye with no blind-spot somehow causes a person to be more likely to have offspring than a person with a blind-spotted eye then perhaps there would be selection pressure. Otherwise it won't make a bit of difference from an evolutionary point of view.

It's not that simple. Something like a blind spot can't just be evolved away. There needs to be a pathway from "has blind spot" to "doesn't have blind spot" that doesn't go through "vastly decreased eyesight" along the way. Otherwise evolution will stick with what it has, and no amount of selection pressure can cause it to change.

We're vastly suboptimal in many ways. We're not perfectly tuned machines, we're cobbled-together from evolutionary scraps, and you can see it by looking at any part of our physiology. That's precisely the thing that makes intelligent design a stupid idea. Yet, we "work", and are capable of survival, and that's enough.

There are people who say that each organism is 'perfectly adapted' to its environment. I never understood them because you don't even have to look hard to find out that that is not true. Besides, if they were they would be extinct as soon as their environment changed only the tiniest bit.

To be fair, though, it's possible to be perfectly adapted to your environment but also well-adapted to other environments (not that any creature is). It's also possible to be only slightly adapted to your environment but even less adapted to any other environment. Indeed, it's also possible to be well-adapted to your environment and to go extinct through just pure chance, without your environment changing at all. Darwin actually talked about that in The Origin of Species. A tree might produce hundreds of th

You can even argue that 'perfectly adapted' means they don't have to reproduce because having to reproduce means that you die, and that means that the environment in which you live is not good for you. So 'perfectly adapted' is incorrect on many levels.

The blind spot appears because the light sensible cells are built in reversely. Their connection to the brain leaves the cells from the outside, e.g. from the skin side of the cells. Thus this eye needs a place where the nerval connections cross the light sensible area again to get to the brain. This place, where the nerves crosses the retina is the blind spot. This is a general flaw in all vertebrate eyes.

Cephalopod eyes have no blind spot. Perhaps the fish that spend more time at the surface had different evolutionary pressure (more light).

The blind spot appears because the light sensible cells are built in reversely. Their connection to the brain leaves the cells from the outside, e.g. from the skin side of the cells. Thus this eye needs a place where the nerval connections cross the light sensible area again to get to the brain. This place, where the nerves crosses the retina is the blind spot. This is a general flaw in all vertebrate eyes.

Had the eye been intelligently designed, you could run them radially out, then around the back to the brain, rather than making a blind spot. Well, that and the issue of the light blocked by the connections running in front if the sensors, a problem the Cephalopod eyes don't have.

Or, you know, take a further lesson from the cephalopods and reverse the retinal cells so that the sensors are directly on the imaging surface instead of being buried under several layers of infrastructure. That would allow you to use much less sensitive detectors as well.

The problem with less sensitive is that they are less sensitive. Ours are about as sensitive as physically possible. It doesn't take much for a rod to fire. So what happens when you have less sensitive ones? To they fire exactly 1/10th of the time for the same amount of light? Do they increment their hit counter once every 5-20 photons, with a random sensitivity variation that could result in new and unexpected artifacts? Does the greater covering (by wiring) around the dense areas work well with densi

As for sensitivity - really what difference would you expect it make whether the sensor was 10% as likely to respond to an individual photon, or if it responded to every photon that reached it, but 90% of them got absorbed by the layers of other tissue between it and the light source instead? Either way you're responding to 10% of the photons that make it to the retina. (though I would guess the actual number is higher than 10%)

Some people already have significant issues with flicker. And a non-detrministic result would have other effects (our eyes trigger on every event), perhaps it would decrease speed estimation or motion detection.

It's not a big flaw since it makes it easier to have and maintain the tapetum lucidum or retinal pigmented epithelium and still have relatively high resolution.

Thing is even intelligent designers can create optical stuff with flaws.

For example reflecting optical telescopes have flaws since the detector (or secondary mirror) part is in between the mirror and the target AND the detector also needs support structures. These block and distort light. https://en.wikipedia.org/wiki/... [wikipedia.org] But most astronomers accept a

To me consciousness is just memory and the ability to make decisions based on old memories. "Couldn't the whole universe work like it does without it existing". Yes sure it could, for simple lifeforms you really don't need consciousness, just look at plants they don't have consciousness and are just programmed with specific reactions to specific circumstances. But for complex lifeforms that need to adapt and survive in complex environments I think consciousness is a necessary trait to have to be able to rea

Suppose you provide some sort of scientific definition of "consciousness". Right now, the word is used extremely vaguely, and it's really hard to tell what it means. If your definition is good enough to tell whether a cat does or does not have it, it's probably good enough to see if there's any evolutionary advantage and what path it took.

Though it might not be a flaw. As Nick Lane points out, evolution is cleverer that you are. For example, the nerves that cross the front of the retina could have evolved to act as wave guides improving vision, not making it worse compared to say, the eye of an octopus which is "correct" as you might design it.

you are silly, vast differences in eyes in the animal kingdom. the spookfish eye has a side chamber with mirrors and a second retina, and works like a reflecting telescope. The Tarsier can't even move its eyes in the sockets, has to turn its head, besides night vision can see in ultraviolet but can't see color. The collosal squid has a built-in headlight, a photophore, in each eye to illuminate what it is focusing on, the dragonfly has 30,000 eyes that can see polarization of light as well as ultraviolet let, and moreover has 3 additional eyes of another type that are hypersensitive to extremely fast movements a human can't perceive. How about four-eyed fish with eyes to see in air and another pair for water?

Don't forget lobster eyes, very cool design - lots of square mirror boxes. They are even planning an x-ray analog of them at Nasa [nasa.gov]And the lowly scallop has a very nice set up to about 100 reflectors 1 mm in size.

also could have mentioned some bird's eyes that can see the earth's magnetic field; and goats with their horizontal rectangular pupils, which combined with the eyes position on the skull gives them a 340 degree field of vision without even having to move their eye. they can see you coming up behind them!

I have to say as a complete layman that I find this whole discussion fascinating. I had no idea there was such a wide variety of eyes in this world.

Which makes me wonder though why we haven't actually been seeing any/many inventions making use of these principles to augment our own vision. For example, I can see that a physical analog for the goat's vision may have some application in the field of law enforcement, or vehicle HUDs or anything for that matter where a larger field of vision would be an advant

Which makes me wonder though why we haven't actually been seeing any/many inventions making use of these principles to augment our own vision. For example, I can see that a physical analog for the goat's vision may have some application in the field of law enforcement, or vehicle HUDs or anything for that matter where a larger field of vision would be an advantage.

also could have mentioned some bird's eyes that can see the earth's magnetic field

Why does everyone overlook the fact that the eye is a device that leverages quantum mechanics? The simple fact that we can observe the electromagnetic spectrum is proof of this. By extension, it would be reasonable to conclude that the brain also leverages quantum mechanics.

The tarsier and 4 eye fish are remarkbaly cool, but they are variations on the vertebrate eye, which means they're much more similar even to each other than the various types of invertebrate eye. The interesting thing of course is that the various ranched all evolved eyes from very different starting points.

Also if you want awesome eyes, look at the the mantis shrimp. Hyper spectral, polarisation sensitive and capable of independent depth perception (trinocular, not binocular like us mere vertebrates) with

The key question is whether the same results would come from different ends, again.

And the key evidence is that parallel evolution uses different changes from different genes to achieve the same end.

The question that I have to ask is, if different changes result in the same end, can the follow-on changes result? Or are they stopped?

Flippers turn into hands, but using different gene combinations - does that stop the thumb from differentiating? Or would evolutionary pressure still reward the mutant with the thumb?

I haven't read the whole thing, but I'm not swayed on any part of the question other than someone is now thinking about this. It is far from the foregone conclusion you think it is. In fact, in your statements, it stops at the interesting point. Will eyeballs that evolved differently be able to further evolve in similar ways? Or are they forever doomed, due to their makeup of different proteins, to be different? Or is it somewhere in the middle, which sounds plausible pending further research?

I think the answer is self-evident: alternate reality results would be just as diverse as species are today, and while they would bear superficially similar results, they would be "different animals." Commenters above have noted that vastly diverse organisms in a common environment still successfully evolve common features: they may have similar means of locomotion, means of food detection, means of sexual partner selection, and on and on, yet the specifics for any given species will be completely different from the other species.

Would the appearance of an opposable thumb on a flipper cause the lengthening of the appendage into something more useful, like an arm? Maybe, because arms are a useful advantage for food gathering; or maybe not because arms aren't as hydrodynamic as flippers. Or maybe there'd be a fork with two successful species resulting. I don't think the follow on changes would stop, they just would be different changes.

But as to the original article, why would anyone think that if we rewound the clock that a chaotic process would repeat? It's not like the universe called rand() with a common seed when it started mutating DNA.

But as to the original article, why would anyone think that if we rewound the clock that a chaotic process would repeat? It's not like the universe called rand() with a common seed when it started mutating DNA.

It's a valid question, when looking to the simplest organisms such a viruses or bacteria you can observe repetition of specific adaptations when under the same environmental pressures (up to a certain point). You neutralize several strains with monoclonal antibodies or a compound against a specific protein and the escape mutants frequently show the same changes. The question is "how much of this is conserved in more complicated organisms?" It would not be the first time that an apparently chaotic process wa

Forgive me for trying to boil this down into more simplistic terms to understand the concept:-

So what you're saying is that just because 2 different drivers drove from Town 1 to Town 2 (similar results), it does not necessarily mean that they took the same route. Driver A had to buy groceries, pick up his daughter, visit the video store so he drove a certain route. Driver B had to top up his gas, return a library book and buy dinner so he took a different route (evolutionary pressures). But both of them end

Actually no. Because both drivers had to use their respective route again if they drive again from Town 1 to Town 2. After some generations you would have two different tribes of drivers, one that drives along the grocery store and the kindergarden, the other one via the gas station and the library. And if the video store closes, some drivers of the first tribe cease to drive at all because it doesn't make sense to them anymore while the new hardware store causes other drivers of the first tribe to morph in

That's not really a good analogy, because your drivers have "goals", and evolution doesn't drive towards goals. It selects for adaptations that work better in the organism's environment.

Driver A isn't trying to get to Town 2. Driver A simply is trying to survive. Now, if your Driver A randomly developed a vision mutation that caused him to identify grocery store signs, that's a beneficial survival trait in his environment - he'll be big and healthy and not starving, which might make him a more successful

Not taking into account interaction between random changes in different species. Change is random, but natural selection is not, if your random changes make you survive and breed, they may remain enough time to become evolution of your species. But if a random change in a prey (or a predator) turns into viable a random change in a predator (or viceversa) then you could get something new, same for environmental changes. Is not a butterfly effect, but is enough to not make very predictable the course of evolu

Sharks and whales are interesting in that they look similar, but are quite different. One breaths air while the other has gills to breath water. Also, the whales have a horizontal tail-fin and their propulsion motion is an up and down wave while the sharks are based on a fish body plan with a vertical tail-fin and their propulsion motion is a side to side wave.

Convergent evolution suggests it is somewhat predictable, unrelated species having evolved similar solutions to similar problems. If a solution is clearly better nature will tend to go there given sufficient time and experimentation (mutation).

The fact that a trait may be expressed by different DNA sequences doesn't really seem to undermine this. The DNA sequences are implementation details. Evolution is about solutions and environments not DNA sequences.

The fact that you have widely different 'implementation details' solving similar problems suggests that it's NOT as deterministic a process as your'e suggesting.

Nature exerts a strong evolutionary pressure on animals that can *sense the environment around them.* One good way of sensing the environment around you is a complex "camera eye" - but there are many ways of implementing this in multiple organisms, which means that minute variations in environment can have a large effect on evolutionary outcomes.

Who said it is a deterministic process? Evolution is based on random mutations. All that is being suggested in that given a large number of experiments a more optimal solution tends to be found, if one exists. That similar environments can independently converge (discover) upon such a solution. Its not unlike multiple independent runs of a Monte Carlo simulation finding the same maxima.

One good way of sensing the environment around you is a complex "camera eye" - but there are many ways of implementing this in multiple organisms

I wonder if an insect-like compound eye is competitive at a larger scale. It seems to me it may be more damage-resistant in that it fails incrementally (spots), where-as a single-chamber design like ours can be taken out of commission if just one part fails.

Well, we do have 2 eyes such that we have 1 spare, but we lose stereo sensing if one goes out. In compound e

Convergent evolution also depends on how you define two features similar. For example, the convergent evolution of oxygen carrying blood in Cephalopods could be a counter example to the prediction argument, as their blood has oxygen bind to copper.

So both bloods were evolved to perform the same task of moving oxygen, however they use two different mechanisms to perform the task.

I think in this situation, by "is evolution predictable" they mean "is evolution reasonably deterministic with respect to creating a given set of genetic code given a set of starting code and a certain environment".

The degree of molecular similarity in the DNA changes to achieve a particular result will depend strongly on the type of change one is looking at.

For the case of toxin-resistance, which is much closer to the molecular level, the odds of similar changes to the DNA are much higher than for complex morphological changes.

Molecular changes like toxin-resistance are more likely to involve a single gene that codes for a single enzyme, changing the enzyme so that the toxin is no longer metabolized in a harmful way. There are going to be a very limited number of ways to do this because it's pretty close to a one-gene/one-enzyme mapping in many cases.

Morphological changes, on the other hand, involve a whole network of genes that are turned on over the course of development, and the network can be altered in many different ways to get to the same result. Think about it like a road network where you're used to taking a particular route to get from A to B. If a bridge goes out on your your usual route, you may choose different alternatives depending on time of day, the kind of vehicle you drive, etc. Networks create choices.

Even then it will depend on the kind of morphological change we are talking about.

For example, there is a lizard in Mexico, which was studied in the '80's or '90s. There were several related species living inland, and a couple of isolated species on the coast near the Yucatan peninsula. Both the coastal species had an extra cervical (neck) vertebra, and it had been assumed on the basis of this similar morphology that their evolutionary history had been a general migration to the coast, an adaptation to coastal environments that involved having a longer neck, followed by a general die-back that resulted in the two existing but separate populations.

It turns out based on their genes the two coastal species hadn't had a common ancestor for millions or tens of millions of years, and the adaptation to coastal living had happened independently but fairly recently. In this case, because certain aspects of body plan are controlled by a highly conserved and relatively simple set of genes, the additional vertebra were the result of similar sets of genetic changes.

Things like body width, which is what TFA is talking about, are a lot more complicated in their regulation, so more likely to be achieved via different genetic changes that have the same morphological outcome.

I'm going to throw in a shameless plug here because it seems relevant to the topic at hand. I've just published a hard SF novel that's premised on a what-if about the role of mathematics and law-like descriptions in evolution. If you're interested in that sort of thing you should check it out: http://www.amazon.com/Darwins-... [amazon.com]

Is your book available in print form? I only see the kindle edition. Also, it would be great if you could put your email address on your profile so I don't have to reply to your comment in order to contact you:P

...researchers have found that although groups of the bug have evolved similar appearances, they achieved that mostly via different changes in their DNA. 'I think it says that repeatability of evolution is very low...

I read this as "Stick bugs have reached similar appearances through different means thus the same change probably won't make the same result".

Is this equivalent to "People can change their appearance to include a hole in the abdomen through different means (bullets and knives). Thus shooting or stabbing people are unlikely to produce holes in people"?

It may make it more difficult to guess which DNA change caused them to look like that (without an actual DNA test), but it in no way implies that those DNA changes won't necessarily cause them to look like that.

Yes you are reading that wrong. What they are saying is that since you can end up with similar looking creatures that took different DNA routes to get there, it's only the results that matter and not the DNA framework.

If you can end up with the same body style with different DNA then if you rewind the clock and started over there would be no reason to believe that you would end up with the same creatures we have today.

The summary was a little confusing. When they said "wound the clock back", I thought they were talking about re-implementing the same mutations and expecting a different result, not animals conforming to similar situations via different mutations.

Ok, I think I get it now. So they're not saying we probably wouldn't end up with animals that look like they do today, but that we would likely end up with the same looking animals with different DNA than we have now. That actually makes a lot more sense.

Now, we watch all the original developers quit, and we hire more developers to deal with changed specs. What they do is likely to depend heavily on which version of the code we give them. If the specs are more like "Make the code do this general thing", we're likely to wind up with different-looking solutions.

Looking at cows, dolphins and horses genetic proximity [ucsc.edu] shows unexpected results, as cows and horses are not the closer in the trio, despite their similar features.

That suggests environment drives evolution in a predictable way, while the genetic evolution is not. This is the really amazing point: evolution find similar solutions to similar problems, but it does so through different ways.

This is the really amazing point: evolution find similar solutions to similar problems, but it does so through different ways.

This is a common problem when talking about evolution. We can't help invoking metaphors of "design," even if we don't mean it -- and that clouds our understanding.

Evolution is not "finding" anything. It is not a conscious process. If we truly believe that evolution works through random genetic mutation, that it is simply a matter of randomness and survival of random things that fit the environment better.

If I program a robot to randomly drive around a maze, it will eventually get to the end over a lo

I could say that evolution finds solution to environmental challenges like water finds the way out of a bucket.

But let me rephrase what I find amazing : evolution leads to the same solutions for the same environmental challenges, but through different genetic setups. That suggests the optimum is always reached. This is amazing.

Refer to Stephen Jay Gould and his "Wonderful Life" http://en.wikipedia.org/wiki/B... [wikipedia.org] also. Gould mentions that there were a range of various paleobiological doohickeys bopping around at the same time, and we come from one group that happened to swim better, or whatever. Next time round, we'll have five eyes.

We need to see how things evolved on other worlds, evolving entirely independently of the life forms on this planet, which may have in some way influenced eachother, in order to even begin to gauge how predictable evolution is.

We know precious little about how evolution proceeded here, and we know nothing at all about how it might have proceeded elsewhere.

We can guess that it would be carbon based, because carbon has four covalent bonds and would have been formed sooner than silicon (with 4 bonds, but lower energies) would have. Beyond that, we'd need a few dozen D20 dice to calculate the odds.

But any real scientist knows that at some point, we have to admit WE DON'T KNOW how it might turn out. Wild-assed guesses aren't science

Can we get a Star Trek like movie but instead of meeting human looking weirdos in outer space, let's meet species that look really weird, yet make friends with us and we commnunicate. Like Octopuses, and Snake-people, bug-looking-people, birds with intellect, Koala bear looking chess players, etc.

not imaginative enough. Life in outer space would be less similar to us than bacteria on Earth is (so bird-like and octupus like is too "tellocentric"). Having said that, certain body plans are likely to reoccur like light sensors (eyes have developed several times independently on Earth) likely close to the proccesing unit ("brain", could also be distributed like in an octopus) and feeding organs.

There's a great book by the artist Wayne D. Barlowe, called "Expedition". it shows the life forms of a fictional planet called Darwin 4 . With dense atmosphere and low gravity, Everything evolves big, and almost nothing has anything like eyes (sonar is both popular and often very advanced). Without giving too much away for those who still haven't run across this, there are several common body plans that tend to run through whole phyla, and which don't occur on Earth, but make really good sense on Darwin 4. The underlying science is generally sound - I base this on the way various people who have read it point to this or that creature as less probable than the others, but seem to pick out different ones. This book has become my standard for SF aliens.

There is a tv special made based on that book called Alien Planet. I had not heard of the book before you mentioned it, but I recognized the name of the planet and the strange types of creatures on it. It was interesting even though it is all made-up speculation and there is no real science in it. It is on Netflix if any one wants to check it out. I particularly liked the ideas on how the remote AI flying rovers would be designed and programmed each with a slightly different personality so they won't all be

Hmm, sonar actually seems like a poor choice for one important reason: it's *active* - meaning that in order to be able to "see" something you basically have to scream at it, which would make both hunting and fleeing predators far more difficult since stealth is not an option. Meanwhile the very first creature to develop even crude imaging eyes would have a massive advantage. Also, it's considerably more complicated, so unlikely to prove a viable means of detection until the organism has independently dev

I can see this point several times over. For instance, if complex animals developed on land before sea, perhaps we would have a eye better suited for terrestrial conditions instead of one that has to work in suspended aqueous solution. A terrestrial eye would benefit a great many species. Instead we managed to get this one trait passed on from generation to generation only modified to work in the existing environment. The downside of complex evolution is once you have committed to a certain path, gettin

Solaris (book more than movies) is IMHO just about the only popular SF that's pointed out plainly that aliens are likely to be truly alien. Most of the book is about how a vast amount of work in a century since contact did little other than reflect the views the researchers had before they even came in contact with the alien/s. Even with godlike powers the alien/s couldn't get a message through from the other direction either.Greg Egan had another approach where a chain of cloned and increasingly altered

Sector General: The TV Series! I'd watch the shit out of that show. There are few concepts that allow for multiple truly alien species all living and working together that don't involve exploration and warfare; a massive hospital space station built for the express purpose of intercultural contact is a brilliant way to do it.

Can we get a Star Trek like movie but instead of meeting human looking weirdos in outer space, let's meet species that look really weird, yet make friends with us and we commnunicate. Like Octopuses, and Snake-people, [and...]

No. Because biology (even xenobiology) is biology and budgets are budgets. And never shall the twain shall meet (other than via an NSF grant).

Anyone besides me ever do the high-school biology experiment where you zap some fruit flies with Xrays and observe well-known malformations in their offspring? While there are random mutations, some are far more likely than others under any specified conditions.

However, the properties of a mole of Nitrogen atoms in a jar
has extremely PREDICTABLE properties.

So it is not inconceivable that a LARGE number of organisms
undergoing RANDOM changes may have PREDICTABLE
traits at the end of a long period. Mutations that cause DEATH
will be quickly weeded out of the population, for one thing.
Mutations that do not support survival would go away after
a short time as well.